Mobility Scooters Explained
Electric footpath scooters are powered by batteries. They are a simple vehicle with few working parts, requiring a relatively low level of maintenance. These mobility scooters come in three or four wheel versions and are primarily designed for use on footpaths, with the 3 wheel models more suited to inside use because of their maneuverability.
In general, mobility scooters have a maximum speed of less than 10 kph (the most common maximum speed allowed for a mobility scooter). They are activated by a simple throttle, operated by the fingers, which controls both speed and braking. Steering is via a variety of types of handlebars that operate in a similar fashion to push bikes or motor bikes. They come with varying equipment levels, from twin headlights, blinkers, “bull bars”, even independent suspension, down to basic machines with simple controls.
Batteries. All modern mobility scooters are powered by 2 x 12 volt batteries. These can be either wet or dry cell batteries, but few scooters these days use wet cell batteries.
Batteries in mobility scooters are not like car batteries in that they are a deep cycle battery. These batteries are rated in Amp Hours – ie how many hours a battery will run when one amp is drawn in power. This rating will determine (along with the efficiency of the motor) the range a mobility scooter will travel between charges. The higher the rating, the longer the scooter will run, given similar conditions. Hills and weight load, as well as the surface and the age of the batteries will have an effect on range.
Dry cell batteries come in two basic types: Sealed Lead Acid (SLA’s) and Gel Acid. Both types are maintenance free. SLA’s are cheaper than Gel batteries, but Gel batteries have a longer life.
Motors. Almost all mobility scooters use either 12 volt or 24 volt motor. Usually if there are two motors, they are 12 volt in series; if there is one motor it will be 24 volts. There are different ways of rating the power of a motor. Most manufacturers rate their motors in continuous watts – usually over a period of 30 minutes. A few manufacturers use a different method, sometimes called “stalled” power. This usually gives a power rating of about 2 – 2.5 times the method using a continuous rating. Comparing one scooter’s power with another is therefore not easy if you don’t know whether the watts are a continuous rating or not. In general, most scooters draw between 300 and 600 watts of continuous power. One horsepower is 745 watts. The more watts drawn – ie power used – the less distance the scooter will travel on a given battery rating.
To give you a basic idea of power, a large golf cart (that weighs 350 kg unladen and takes a payload of two people + golf clubs, and travels on grass at 20 kph) has between 2 and 3 horsepower – continuous. A mobility scooter weighs between 55 – 80kg.
The actual pulling power of a mobility scooter is determined by both the power of the motor and the type and power of the electronic controller (see section on electronics below).
Drive. To get the power from the motor to the wheels there are different methods:
(a) Gear box differentials. In general, differential drives are expensive to produce and are mostly available in higher volume scooters or because a manufacturer has outsourced the component. These are the most reliable drive, and most resemble a motor car. Mobility scooters with these types of transmission are the most common.
(b) Chain and belt drives. These are less popular than when scooters were first developed – sometimes they require more maintenance than gear boxes, especially in adjustments caused by stretching or breaking. Very few modern scooters use chain drives.
(c) Other gear systems. Several scooter manufacturers who cannot afford a differential gear box (similar to motor cars) may opt for two motors. They use various methods of getting the power to the wheels like chain or belts, but mostly two gear boxes that use either helical gears (stronger but noisier) or worm gears (quieter but not as strong). In addition, a few mobility scooter manufacturers use front wheel drive for their drive system, but generally traction is not good enough for anything but flat areas and indoors.
There are three main braking systems on a modern mobility scooter:
(a) Regenerative. All modern mobility scooters use this as their main method of slowing down or holding a speed on a downhill slope. Here, the motor simply turns into a generator and recharges the batteries (at about 20% of the rate it uses when on a flat), and this generating function turns the motor into a brake at the same time. This is what most mobility scooter manufacturers refer to as “automatic braking”.
(b) Electromagnetic. This refers to the parking brake that is automatically engaged when the scooter is either stopped or nearly stopped. It works by preventing the motor from turning. To free wheel a scooter, either this brake must be disengaged – usually by activating a switch, or by putting the scooter into the neutral gear (if it has a gear box).
(c) Manual. Although not necessary, some scooters have a third braking system – some kind of manually operated brake. Sometimes this is simply a “billy cart” style brake that rubs on the tyre, but more common is a more sophisticated system that works on the axle – eg drum brakes or disc brakes. Scooters sold in Europe are required to have some kind of manual “emergency” brake to comply with the tough European standards.
Electric Mobility Scooters are battery powered. To charge these batteries, the scooters either have an inbuilt charger or a separate charger. These two methods have different advantages. “On board” chargers allow the owner to take the scooter on holidays without having to take a separate charger with them. Separate chargers however, have the advantage of keeping the weight of the scooter down, are less likely to break down because they are not subject to vibration, and if they do fail, the scooter doesn’t have to be immobilised while the charger is repaired – a new charger can be quickly substituted without disruption.
Wet cell batteries are less fussy and therefore can be charged with a cheap charger – usually 12 volt in series. Dry cell batteries need a more accurate charger and usually come in a 24 volt 4 amp configuration. When higher amp hour batteries are used it is advisable to use a 6-8 amp charger. Most “smart” chargers are automatic and either cut out altogether when the battery is charged, or drop to a “trickle” or “float” charge (about 200-300 milliamps). The second method is preferable as this will keep the battery at 100% until the scooter is used.
All modern mobility scooters have a “black box” – ie a sophisticated electronic controller. These control the speed of the scooter (no matter how heavy the payload), the acceleration and braking rates, and apply the parking brake. They also have a major impact on the power of the scooter, depending on the ampere rating of the controller and the amount of current the controller feeds to the motor. Two identical motors can perform very differently when controlled by different electronic controllers.
There are a small number of major controller manufacturers in the world – Curtis (made in U.S.A.), Dynamic (made in N.Z.), P&G (UK) are three of the more well known. Some mobility scooter manufacturers use their own controller or a locally made one. When a controller malfunctions it is expensive to repair and is usually discarded for a new one (it is usually cheaper if the controller is one of the more common ones). Some controllers are programmable to alter speed, acceleration and deceleration rates and other variables. Some controllers also turn the scooter off when it is left unattended for a period of time (“sleep” mode). Care must be taken when connecting batteries or plugs so that no electrical short is caused, thus damaging the controller.
All mobility scooters for the elderly have some sort of finger accelerator to activate the electronics and consequently the motor and brakes. These controls work a potentiometer that gives an infinitely variable speed. These are either of the Wig-Wag style (Neo, Invacare, Shoprider, CTM, etc)- where the forward and reverse function is operated by the one lever that is operated by either hand – or by using a switch to determine forward and reverse and operating the accelerator with the same action by the same hand. Some accelerators are operated by the thumbs, others by the fingers. few operate with either. There is usually some sort of “cruise control” that sets the maximum speed that the accelerator can activate. This may be in the form of a knob or a switch, or some form of touch button system.